1. Purpose of the Invention
This invention relates in general to certain new and useful improvements in hot gas engines, and, more particularly, to hot gas engines which have a first crankshaft connected to the expander portion of the engine and a second and separate crankshaft connected to the displacer portion of the engine and which crankshafts are synchronized in operation.
2. Brief Description of the Prior Art
Hot gas engines, often referred to as "Stirling" engines, have been known for a long period of time. Generally, the Stirling engine comprises a pair of pistons, including an expander piston and a displacer piston, both of which are connected to a single crankshaft. A heat exchanger is connected between the expander portion of the engine and the displacer portion of the engine. In the expander portion of the engine, hot gas is expanded and converts heat energy into power, so that the overall engine produces a useful power output. The displacer portion of the engine utilizes some of the power from the crankshaft to compress a cooled, working gas, thereby generating a net power output from the engine.
The typical Stirling engine is constructed so that a fixed and predetermined phase angle exists between the power piston and the displacer piston in the engine. When the phase angle between the displacer piston and the power piston is 0.degree., there is no power output from the engine. Increases in a positive direction of the phase angle between the displacer piston and the expander piston result in a net forward power output from the engine. Correspondingly, a phase angle change in the opposite direction results in a net reverse power output. Thus, at a full 90.degree. phase angle difference between the expander piston and the displacer piston, full forward power is obtained, and with a -90.degree. phase angle between the expander piston and the displacer piston, full reverse power is obtained from the engine. In this way, it is possible to control the engine's power output and also to change the output to a forward or reverse direction. However, in each of the prior art devices, the displacer piston and the expander piston operated on a common crankshaft and a complex system was required to change the phase between the displacer portion and the expander portion.
It had previously been assumed that the expander piston and the displacer piston must be connected to a common crankshaft in order to obtain efficiency of operation in a Stirling-type engine. For example, in U.S. Pat. No. 3,751,904 to Rydberg, an expander cylinder and displacer cylinder are arranged in side-by-side relationship in the same vertical plane. The expander and displacer piston rods are connected to a common crankshaft through a rather complex linkage arrangement, including crank elbows. In U.S. Pat. No. 3,939,657 to Postema et al., a Stirling engine is provided in which the expander and displacer pistons are connected to a swash plate. The swash plate is, in turn, operatively connected to a power output shaft providing power to the output shaft. In U.S. Pat. No. 4,019,322 to Meijer, a Stirling engine is disclosed in which the cylinders, such as the expander cylinder and the displacer cylinder, are mounted in side-by-side relationship. The pistons in each of these cylinders are connected to a common swash plate and provide power to an output shaft. Moreover, phase angle displacement between the pistons is accomplished by displacement of the swash plate. In U.S. Pat. No. 2,484,392 to Van Heeckeren, a Stirling engine is also provided in which the cylinders, such as the expander cylinders and the displacer cylinders, are mounted in side-by-side relationship. Again, the pistons of these cylinders are connected to a common shaft by means of a conventional piston rod assembly.
The existing hot gas engine, such as the Stirling engine, have not received widespread consideration as a power source in vehicles requiring compact engine design, as for example, automobiles and similar vehicles, due to the size and shape of the typical Stirling engine. The Stirling engine is relatively high compared to its width and length. Therefore, any vehicle using the Stirling engine as a power source must have an engine compartment especially designed to accommodate this type of engine configuration, and the engine compartments in most vehicles, such as automobiles, are not adapted to contain a typical Stirling engine.